@editor Daikin’s usual reply is ‘Ask your installer’ - hope you can fare better than this Mars! Regards, Toodles.

@ubert767 @toodles @bobflux @editor @optimistic-optimiser 

Having had a trawl through OpenEnergyMonitor I found a useful page that gives some real time data around the electricity consumption fluctuating that may be of interest.

If you click on the chart icon to the right of "Approved you can see the detail. In all cases (bar one which I am very interested in!) show the same micro cycling (not full cycling) of the power, which is the same behaviour as ours. If you click on the picture it will take you to the page.

https://heatpumpmonitor.org/heatpump/view?id=46

Thanks for this and that might well be showing some of what I am experiencing.  What I'm not sure about is: if the outside temperature increases and the heat pump flow temperature based on the weather compensation curve drops to compensate, whether the Daikin is designed to switch off the compressor (and therefore the blue light on the Madoka goes out), whilst the water still circulates around the radiators (hence the much lower power consumption) until the flow temperature has dropped to that required by the weather compensation curve at which point the compressor starts again and the blue light on the Madoka comes back on.  If so, how is this reconciled with the need to keep the compressor going to maximise efficiency and prevent wear of teh compressor from starting and stopping?  Surely the compressor should be able to just work a bit less hard rathe r than going off or gradually adjust for the change in outside temperature?

The other thing in these numbers that was interesting is row 2.  You might be getting a COP of 7.2, but why would your heat pump be running at all if the outside temperature was 21.2 degrees?   

Here the heat pump runs continuously and generates power, which manifests as DeltaT between flow and return, and is also displayed as "Heat" power in W.

So it is not cycling, which usually means the compressor stops and starts.

It seems the heat pump's power levels are discrete and it is switching between ~2kW and ~3kW when the desired output power is in between. I don't see any problem with that.

@optimistic-optimiser 

The Daikin at the top is Matt Drummond's I'm pretty sure. There is a lot of posts by him trying to optimise and understand his Daikin HP. I followed this for a few months which helped enormously with my decision to choose  the same 8kw Daikin.

I'm pretty sure he now runs on a fixed flow temperature of around 31c.

I suspect this probably shows up as a steady draw, as the HP is not adjusting the flow temperature as the outside temperature fluctuates

The data was taken to see how low certain Heat Pumps modulate. It's one of the reasons I chose the 8kw Daikin as it's power consumption in the shoulder months is very low.

With your Maduka light going out, I wonder if your system is cycling (switching the compressor off), indicated by the blue light going out, or that you have hit the internal temperature sensor limit?

Mine hardly ever cycles and so the blue light is pretty much always lit.

I also turned the brightness level down as low as possible, as the led light gives of a very small amount of heat and can impact the sensitive temperature sensor.

@bobflux 

Yeah, I don't also. I had wondered why Matt Drummond's 8kw heat pump (the one at the top) has a very steady electricity draw. It must be (as I'm pretty sure) because he runs at a fixed flow temperature of 31c all the time.

Mine has fluctuated all day long between around 250-500w and has averaged just under 400w per hour today with no apparent cycling.

I've consumed around 13kwh's today including 2 DHW runs set at 50c in the early hours and 47c just after lunchtime.

I also run the heat pump flow rate 2c higher between 4am and 6am to utilise the off peak rate and get some extra heat into the house.

I am very happy with the consumption levels and the system is near totally silent. I can only hear the low hum of the fan running when very close outside. It is silent inside all of the time.

I can now hear my next door neighbours gas boiler inside our house as it is so noisy compared to the heat pump we have!

@optimistic-optimiser, as promised, I reach out to Daikin and they replied to me this morning. 

Their response was that it’s not something they see commonly, but they suggested two possible explanations for what you’re observing.

The first possibility is that the circulation pump inside the heat pump is still operating even though the compressor has stopped. In that situation you’d still see a small amount of electricity being used, but the outdoor unit would appear quiet because the compressor and fan aren’t running. They mentioned that the pump can sometimes operate on its own simply to keep water circulating and prevent freezing, particularly when temperatures are low.

The second possibility they raised is a configuration issue with schedules. They said that sometimes users or installers change the control mode (for example moving from water temperature control to remote thermostat control) but previous schedules may still exist in the background if they weren’t deleted when the settings were changed. In that case those schedules can still trigger behaviour in the system even though the main control method has been altered.

So in short, Daikin’s view was that it’s not necessarily anything abnormal, but they suggested checking whether the system is simply running the circulation pump without the compressor, or whether there might be legacy schedules still active in the controller settings.

Might be worth having a look through the schedule settings just to rule that out.

Hi Mars, Thanks for reaching out to Daikin.  The first possibility is what is happening, but clearly we shouldn't be in a situation where we are trying to prevent freezing at current temperatures.  I have checked the schedules, and there is only one schedule that has been set (user defined 1) and that is the one that is operating.  Today, the thermostat was set at 19.5 degrees and before achieving that temperature the heat pump first switched of fthe compressor and just left the pump running (as witnessed by the reduced power consumption, but also from the information menu I can see whether the pump and compressor are on) and then it switched the pump off.  Given it is set up with modulation set to 5 and an overshoot of 4 degrees, I cannot understand why it would do this?  It doesn't seem to be able to modulate in middling temperatures which we currently have to keep itself running.  In fact it is behaving more like a dumb gas boiler than a smart heat pump!  Any help greatly appreciated!

Posted by: @optimistic-optimiser

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Thanks for this and that might well be showing some of what I am experiencing.  What I'm not sure about is: if the outside temperature increases and the heat pump flow temperature based on the weather compensation curve drops to compensate, whether the Daikin is designed to switch off the compressor (and therefore the blue light on the Madoka goes out), whilst the water still circulates around the radiators (hence the much lower power consumption) until the flow temperature has dropped to that required by the weather compensation curve at which point the compressor starts again and the blue light on the Madoka comes back on.  If so, how is this reconciled with the need to keep the compressor going to maximise efficiency and prevent wear of teh compressor from starting and stopping?  Surely the compressor should be able to just work a bit less hard rathe r than going off or gradually adjust for the change in outside temperature?

The other thing in these numbers that was interesting is row 2.  You might be getting a COP of 7.2, but why would your heat pump be running at all if the outside temperature was 21.2 degrees?   

est	System	Date	Duration	Flow temp	Outside temp	Flowrate	Elec input	COP	Heat output	Status
1	72	20th Sep 2025 17:13	50 mins	35.8°C	20.6°C	6.7 L/min	350W	7.4	2601W	Approved
2	224	18th Sep 2025 14:28	257 mins	31.2°C	21.2°C	7.1 L/min	290W	7.6	2200W	Approved
3	72	14th Apr 2025 14:06	19 mins	32.4°C	14.4°C	6.6 L/min	331W	5.5	1806W	Approved
4	561	10th Nov 2025 04:11	308 mins	31.8°C	12.4°C	7.0 L/min	346W	5.2	1788W	Approved
5	561	6th Nov 2025 05:42	180 mins	31.0°C	13.8°C	7.0 L/min	310W	5.4	1676W	Approved

With regards to line 2, could it be that the (demand) was not met and although the external temp was 21.2c (some solar gain no doubt) the actual home / room temperature was below the desired temp, this would explain why it would run, I can make ASHP run when outside is 35Deg C, you just create a demand.

I don't know about the blue light thing as we are not a Daikin specialist but it is worth noting for other areas of posts here that compressor and pumps are not the only current draw or power use your shelly device will see, most if not all units (even in the summer) can run a 200w heater tape to keep the oil in the compressor warm and ready for action, these tapes often run in pulses or stages, Ecodan does something a bit different and pulses the coil inside the compressor without running the compressor to create a little heat. This power use is often overlooked and can be noticed by the keenest eyes or the most active efficiency measuring.. Also all of the EEV / LEVs can periodically do little resets before running, again this is like the unit is getting itself ready to run, I am not sure if all units do this but I think most do.  

If with regards to good old short cycling you manage to get a lot more data, often the 1st place to look is the emitter offset of any heat load, its ok to blame the ASHP for short cycling but it is nearly always due to - oversizing, unbalanced emitters, incorrect emitters, incorrect pipework, incorrect flow rates and then maybe some back end programming. To know for sure you need to measure a lot and find someone who can tune your home heating like a Porsche!

These ASHP have little brains and can do things we do not expect but ultimately it is all calculations and programming to make sure the unit it ready to go, achieves the internal temperature required while trying to decide for itself the most efficient way to do it. Throw in an unbalanced circuit or a 12kW ASHP system on 9kW of emitters and half the programme will not work correctly.  

I hope this helps a little...

As with ASHP-BOBBA I do not install Daikin's specifically, but in the past have found them to be somewhat over complicated, often having "hidden" settings in the configuration menu that are not easily deciphered even by a trained engineer. But on face value it shouldn't be just running the  pump to prevent freezing. Whats the exact Daikin model of the unit you have and do you currently have any active 3rd party monitoring software installed that is actually reading the units Modbus terminals.?

Posted by: @optimistic-optimiser

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rely the compressor should be able to just work a bit less hard rathe r than going off or gradually adjust for the change in outside temperature?

Up to a point yes.  However every heat pump (and every boiler) can only turn down so far, ie it has a minimum output (which, in the case of a heat pump, depends on flow temp and outside temp).  If the demand is less than its minimum output then both boilers and heat pumps resort to cycling (ie periodically switching on and off) so that the output matches the demand on average. 

Different heat pumps have different algorithms to control cycling (doubtless the same is true of boilers).  Vaillant, for example, keeps track of 'energy integral' (the difference between target FT and actual FT multiplied by time, measured in degree minutes) to make the decision when to turn back on.  Doubtless boilers likewise have different algorithms.

Posted by: @optimistic-optimiser

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at I'm not sure about is: if the outside temperature increases and the heat pump flow temperature based on the weather compensation curve drops to compensate, whether the Daikin is designed to switch off the compressor (and therefore the blue light on the Madoka goes out), whilst the water still circulates around the radiators (hence the much lower power consumption) until the flow temperature has dropped to that required by the weather compensation curve at which point the compressor starts again

I expect it to continue circulating, at least for a while, in order evenly to dissipate the energy in the water into the house.  As stated above the algorithm for turning back on varies from heat pump to heat pump